A gas turbine is known to comprise a rotor or turbine shaft rotatably supported by a bearing, a compressor portion including rotor blades mounted at the rotor to compress air, a combustor for burning a mixture of fuel and the compressed air, and a turbine portion which converts the energy contained in the burned mixture of fuel and compressed air into mechanical energy to drive the rotor. A gas turbine may for example be used to generate electric energy by driving a generator using the mechanical energy.
In particular, the air compressed by the compressor portion of the gas turbine may flow not only in a compressor air passage leading to the combustor, but also in a gap between the rotor and a stator portion of the gas turbine. Such leakage of compressed air is not desired, because it reduces the amount of compressed air being led to the combustor. Therefore, the gap between the rotor and the stator portion of the gas turbine into which a portion of the compressed air is introduced in an undesired way is sealed to reduce the amount of compressed air introduced into the gap. However, it has been observed that the sealing property of the conventional seals is not satisfactory. An excessive amount of compressed air may leak from the compressor air passage into the gap between the rotor and the stator portion of the gas turbine. Thereby, an efficiency of the gas turbine is reduced.
U.S. Pat. No. 4,993,917 discloses a gas compressor having dry gas seals, wherein a primary dry gas seal adjacent to the discharge end of the compressor is of larger diameter than the corresponding sealing at the inlet end of the compressor so that pressurized gas acting on the respective rotary part of the dry gas seals urges the shaft towards the discharge end of the compressor and thus counteracts dynamic forces on the impeller.
EP 2 053 201 A2 discloses a hydrostatic seal assembly and the corresponding compressor assembly and gas turbine engine, wherein a portion of the primary gas flow is fed through an inner diameter bleed downstream of a blade into a high pressure cavity, which is located radially inward of a vane.
EP 0 532 303 A1 discloses a system and a method for improved engine cooling, wherein cooling air for the support structure within a cavity is obtained by leakage from the compressor discharge air through a labyrinth seal, wherein the portion of the compressor discharge air, which is not directed to the combustor, is throttled through a series of annular restrictions formed radially by a series of rotating labyrinth teeth.
US 2003/0131602 A1 discloses a turbine power plant having an axially loaded floating brush seal, wherein a chamber within a barrel member is supplied with cooling air from the last stage of a compressor by a controlled amount of leakage through labyrinth seal.
WO 02/01046 A1 discloses a sealing system for a gas turbine, wherein air is fed into the inner barrel using the venting piping of the support cushion such as to create a flow of air, which starts from an intermediate stage of the compressor and goes towards the inner barrel.
WO 02/48525 A2 discloses a system to feed cooling air to a gas turbine, wherein the cooling air is taken from a high pressure source and is conveyed to radial accelerators, which give rise to the tangential acceleration of the air in the direction of the peripheral motion of the rotor surface. The cooling air is released into the hollow rotor with a correspondingly reduced outlet radius.
US 2005/0058533 A1 discloses a sealing arrangement for a compressor, that includes a pressurized air supply duct for supplying pressurized air into a leakage pathway defined between a compressor wheel and a housing of the compressor, which leakage pathway leads from the main gas flow path into a bearing area of the compressor, the pressurized air being supplied at a pressure sufficient to ensure that air and gaseous fuel cannot flow from the main gas flow path through the leakage pathway into the bearing area.
There may be a need for a gas turbine providing higher efficiency, in particular providing a higher sealing capacity of compressed air leaking from the compressor air passage. Further, there may be a need for a method for operating a gas turbine such as to improve the efficiency of the gas turbine, in particular to more effectively seal a gap between the rotor and the stator portion of the gas turbine.